RNA Splicing in Plants

Unlike a bacterial gene, a eukaryotic gene's protein-coding sequence is not one uninterrupted stretch of DNA; it is broken up by intervening non-coding stretches. This 'split gene' organisation was discovered independently by Richard J. Roberts and Phillip A. Sharp in 1977, work for which they later shared the 1993 Nobel Prize. The coding segments, called exons, are the sequences that are both transcribed into RNA and ultimately retained in the mature, translatable mRNA, carrying the actual biological information that specifies the protein. The intervening segments, called introns, are transcribed along with the exons into the primary transcript but do not code for any protein, enzyme or structural polypeptide, and so must be removed before a functional mRNA can be produced. RNA splicing is exactly this removal-and-joining process: introns are cut out and discarded, and the flanking exons are stitched together into one continuous coding sequence. The whole reaction takes place inside a large, roughly 40-60 nanometre spherical multi-protein machine called the spliceosome, which is itself built from small nuclear ribonucleoprotein particles (snRNPs), each combining small nuclear RNAs (snRNAs) with associated proteins that together recognise the exact boundaries of each intron and catalyse its precise removal, using a ribozyme (an RNA-based enzyme) to carry out the actual chemist …